Thermoplastic polyurethane (herein TPU) and isotactic polypropylene (herein i-PP) are intrinsically incompatible, except at the lowest levels of incorporation of one resin in the other. It has been suggested that TPU/i-PP blends would offer advantages in terms of cost, hydrolytic and thermal stability, stain and solvent resistance mechanical properties and good adhesion to polyolefin substrates. Blends of these resins are typically delaminated and their mechanical properties are poor. Delamination in the present context means the separation of polymer blend into its components in a molded part. This is evidenced by either the lowering of some measured physical property to a value below that for either one of the components or by visual observation of separation (for instance, fracture or crumbling).
Relevant compositions were disclosed in the article "Polyurethane - Polypropylene Blends", Z.S. Petrovic et al in J. Appl. Polym. Set. 42, 1991 pp. 779; the preparation of these blends was noted to be difficult, especially for blends containing more than 3% polyurethane.
U.S. Pat. No. 3,272,890 discloses blends of polyurethane and polyethylene. The method of preparation of the blend entails melting and fluxing the polyethylene in a Banbury mixer and then adding the polyurethane. Systems containing dispersed polyethylene in polyurethane have been disclosed in U.S. Pat. Nos. 3,310,604; 3,351,676; and 3,358,052; other relevant blends having improved processability have been disclosed in U.S. Pat. No. 3,929,928.
U.S. Pat. Nos. 4,410,595 and 4,423,185 disclose compositions containing thermoplastic polyurethanes and polyolefins, the later being modified with functional groups including carboxylic acid anhydride. Japanese Pat. No. Application 74,9831 (Derwent Abstract 24216V) discloses modified ionomer polymer blends containing polyurethane and polyethylene.
Of particular relevance is U.S. Pat. No. 4,883,837 which disclosed compatible compositions containing a polyolefin, a thermoplastic polyurethane and as a compatibilizing agent, modified polyolefin. The modified polyolefin thus disclosed is an olefinic copolymer containing functional groups.
Instructively, the functional group is part of an unsaturated monomer which is either copolymerized with an olefin monomer or grafted onto a polyolefin to form the modified polyolefin.
It is a purpose of the present invention to provide a resinous mixture useful as a compatibilizing agent in the context of thermoplastic compositions containing polyolefins. It is further an object of the invention to provide compatible compositions containing TPU and polyolefin which compositions exhibit improved mechanical properties.
It is an additional purpose of the invention to provide for a means to produce a resinous mixture useful in the preparation of compatible TPU/polyolefin blends having improved mechanical properties.
It is a further purpose of the invention to provide a thermoplastic molding composition which contains a compatible blend of TPU with i-PP, or TPU with a blend of i-PP and an elastomer (herein TPO), having improved mechanical properties.